Probing correlations of early magnetic fields using μ-distortion

Jonathan Ganc, Martin Snoager Sloth

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

The damping of a non-uniform magnetic field between the redshifts of about 10 4 and 10 6 injects energy into the photon-baryon plasma and causes the CMB to deviate from a perfect blackbody spectrum, producing a so-called μ-distortion. We can calculate the correlation 〈μ T〉 of this distortion with the temperature anisotropy T of the CMB to search for a correlation 〈 B 2ζ〉 between the magnetic field B and the curvature perturbation ζ; knowing the 〈 B 2ζ〉 correlation would help us distinguish between different models of magnetogenesis. Since the perturbations which produce the μ-distortion will be much smaller scale than the relevant density perturbations, the observation of this correlation is sensitive to the squeezed limit of 〈 B 2ζ〉, which is naturally parameterized by b NL (a parameter defined analogously to f NL). We find that a PIXIE-like CMB experiments has a signal to noise S/N≈ 1.0 × b NL ( μ/10nG) 2, where μ is the magnetic field's strength on μ-distortion scales normalized to today's redshift; thus, a 10 nG field would be detectable with b NL=(1). However, if the field is of inflationary origin, we generically expect it to be accompanied by a curvature bispectrum 〈ζ 3〉 induced by the magnetic field. For sufficiently small magnetic fields, the signal 〈 B 2 ζ〉 will dominate, but for μ≳ 1 nG, one would have to consider the specifics of the inflationary magnetogenesis model. We also discuss the potential post-magnetogenesis sources of a 〈 B 2ζ〉 correlation and explain why there will be no contribution from the evolution of the magnetic field in response to the curvature perturbation.

Original languageEnglish
Article number018
JournalJCAP
Volume2014
Issue number8
ISSN1475-7516
DOIs
Publication statusPublished - 1. Aug 2014

Keywords

  • astro-ph.CO
  • gr-qc
  • hep-th
  • primordial magnetic fields
  • non-gaussianity
  • CMBR theory
  • cosmic magnetic fields theory

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